feat(dees-table): add virtualized row rendering for large tables and optimize table rendering performance

changelog.md

@@ -1,5 +1,12 @@
 # Changelog
 
+## 2026-04-07 - 3.66.0 - feat(dees-table)
+add virtualized row rendering for large tables and optimize table rendering performance
+
+- add a virtualized mode with configurable overscan to render only visible rows while preserving scroll height
+- improve table render performance with memoized column and view-data computation plus deferred floating header rendering
+- update the dees-table demo to showcase virtualized scrolling in the fixed-height example
+
 ## 2026-04-07 - 3.65.0 - feat(dees-table)
 add schema-based in-cell editing with keyboard navigation and cell edit events
 

ts_web/00_commitinfo_data.ts

@@ -3,6 +3,6 @@
  */
 export const commitinfo = {
   name: '@design.estate/dees-catalog',
-  version: '3.65.0',
+  version: '3.66.0',
   description: 'A comprehensive library that provides dynamic web components for building sophisticated and modern web applications using JavaScript and TypeScript.'
 }

ts_web/elements/00group-dataview/dees-table/dees-table.demo.ts

@@ -700,7 +700,8 @@ export const demoFunc = () => html`
         <dees-table
           id="scrollSmallHeight"
           .fixedHeight=${true}
-          heading1="People Directory (Scrollable)"
+          .virtualized=${true}
+          heading1="People Directory (Scrollable, Virtualized)"
           heading2="Forced scrolling with many items"
           .columns=${[
             { key: 'id', header: 'ID', sortable: true },

ts_web/elements/00group-dataview/dees-table/dees-table.ts

@@ -199,6 +199,21 @@ export class DeesTable<T> extends DeesElement {
   @property({ type: Boolean, reflect: true, attribute: 'show-selection-checkbox' })
   accessor showSelectionCheckbox: boolean = false;
 
+  /**
+   * Enables row virtualization. Only rows visible in the nearest scroll
+   * ancestor (or the viewport) plus a small overscan are rendered. Top and
+   * bottom spacer rows preserve the scrollbar geometry.
+   *
+   * Assumes uniform row height (measured once from the first rendered row).
+   * Recommended for tables with > a few hundred rows.
+   */
+  @property({ type: Boolean, reflect: true, attribute: 'virtualized' })
+  accessor virtualized: boolean = false;
+
+  /** Number of extra rows rendered above and below the visible window. */
+  @property({ type: Number, attribute: 'virtual-overscan' })
+  accessor virtualOverscan: number = 8;
+
   /**
    * When set, the table renders inside a fixed-height scroll container
    * (`max-height: var(--table-max-height, 360px)`) and the header sticks
@@ -245,6 +260,46 @@ export class DeesTable<T> extends DeesElement {
   @state()
   private accessor __editingCell: { rowId: string; colKey: string } | undefined = undefined;
 
+  /**
+   * True while the page-sticky floating header overlay is visible. Lifted
+   * to @state so the floating-header clone subtree is rendered only when
+   * needed (saves a full thead worth of cells per render when inactive).
+   */
+  @state()
+  private accessor __floatingActive: boolean = false;
+
+  // ─── Render memoization ──────────────────────────────────────────────
+  // These caches let render() short-circuit when the relevant inputs
+  // (by reference) haven't changed. They are NOT @state — mutating them
+  // must never trigger a re-render.
+  private __memoEffectiveCols?: {
+    columns: any;
+    augment: boolean;
+    displayFunction: any;
+    data: any;
+    out: Column<T>[];
+  };
+  private __memoViewData?: {
+    data: any;
+    sortBy: any;
+    filterText: string;
+    columnFilters: any;
+    searchMode: string;
+    effectiveColumns: Column<T>[];
+    out: T[];
+  };
+  /** Tracks the (data, columns) pair that `determineColumnWidths()` last sized for. */
+  private __columnsSizedFor?: { data: any; columns: any };
+
+  // ─── Virtualization state ────────────────────────────────────────────
+  /** Estimated row height (px). Measured once from the first rendered row. */
+  private __rowHeight: number = 36;
+  /** True once we've measured `__rowHeight` from a real DOM row. */
+  private __rowHeightMeasured: boolean = false;
+  /** Currently rendered range [start, end). Triggers re-render when changed. */
+  @state()
+  private accessor __virtualRange: { start: number; end: number } = { start: 0, end: 0 };
+
   constructor() {
     super();
     // Make the host focusable so it can receive Ctrl/Cmd+C for copy.
@@ -368,28 +423,106 @@ export class DeesTable<T> extends DeesElement {
 
   public static styles = tableStyles;
 
-  public render(): TemplateResult {
+  /**
+   * Returns the effective column schema, memoized by reference of the inputs
+   * that affect it. Avoids re-running `computeEffectiveColumnsFn` /
+   * `computeColumnsFromDisplayFunctionFn` on every Lit update.
+   */
+  private __getEffectiveColumns(): Column<T>[] {
     const usingColumns = Array.isArray(this.columns) && this.columns.length > 0;
-    const effectiveColumns: Column<T>[] = usingColumns
+    const cache = this.__memoEffectiveCols;
-      ? computeEffectiveColumnsFn(this.columns, this.augmentFromDisplayFunction, this.displayFunction, this.data)
+    if (
+      cache &&
+      cache.columns === this.columns &&
+      cache.augment === this.augmentFromDisplayFunction &&
+      cache.displayFunction === this.displayFunction &&
+      cache.data === this.data
+    ) {
+      return cache.out;
+    }
+    const out = usingColumns
+      ? computeEffectiveColumnsFn(
+          this.columns,
+          this.augmentFromDisplayFunction,
+          this.displayFunction,
+          this.data
+        )
       : computeColumnsFromDisplayFunctionFn(this.displayFunction, this.data);
+    this.__memoEffectiveCols = {
+      columns: this.columns,
+      augment: this.augmentFromDisplayFunction,
+      displayFunction: this.displayFunction,
+      data: this.data,
+      out,
+    };
+    return out;
+  }
 
-    const lucenePred = compileLucenePredicate<T>(
+  /**
-      this.filterText,
+   * Returns the sorted/filtered view of the data, memoized by reference of
-      this.searchMode === 'data' ? 'data' : 'table',
+   * everything that affects it. Avoids re-running the lucene compiler and
-      effectiveColumns
+   * the sort/filter pipeline on every render.
-    );
+   */
-
+  private __getViewData(effectiveColumns: Column<T>[]): T[] {
-    const viewData = getViewDataFn(
+    const searchMode = this.searchMode === 'data' ? 'data' : 'table';
+    const cache = this.__memoViewData;
+    if (
+      cache &&
+      cache.data === this.data &&
+      cache.sortBy === this.sortBy &&
+      cache.filterText === this.filterText &&
+      cache.columnFilters === this.columnFilters &&
+      cache.searchMode === searchMode &&
+      cache.effectiveColumns === effectiveColumns
+    ) {
+      return cache.out;
+    }
+    const lucenePred = compileLucenePredicate<T>(this.filterText, searchMode, effectiveColumns);
+    const out = getViewDataFn(
       this.data,
       effectiveColumns,
       this.sortBy,
       this.filterText,
       this.columnFilters,
-      this.searchMode === 'data' ? 'data' : 'table',
+      searchMode,
       lucenePred || undefined
     );
+    this.__memoViewData = {
+      data: this.data,
+      sortBy: this.sortBy,
+      filterText: this.filterText,
+      columnFilters: this.columnFilters,
+      searchMode,
+      effectiveColumns,
+      out,
+    };
+    return out;
+  }
+
+  public render(): TemplateResult {
+    const effectiveColumns = this.__getEffectiveColumns();
+    const viewData = this.__getViewData(effectiveColumns);
     (this as any)._lastViewData = viewData;
+
+    // Virtualization slice — only the rows in `__virtualRange` actually
+    // render. Top/bottom spacer rows preserve scroll geometry.
+    const useVirtual = this.virtualized && viewData.length > 0;
+    let renderRows: T[] = viewData;
+    let renderStart = 0;
+    let topSpacerHeight = 0;
+    let bottomSpacerHeight = 0;
+    if (useVirtual) {
+      const range = this.__virtualRange;
+      const start = Math.max(0, range.start);
+      const end = Math.min(viewData.length, range.end || 0);
+      // On the very first render the range is {0,0} — render a small first
+      // window so we can measure row height and compute the real range.
+      const initialEnd = end > 0 ? end : Math.min(viewData.length, this.virtualOverscan * 2 + 16);
+      renderStart = start;
+      renderRows = viewData.slice(start, initialEnd);
+      topSpacerHeight = start * this.__rowHeight;
+      bottomSpacerHeight = Math.max(0, viewData.length - initialEnd) * this.__rowHeight;
+    }
     return html`
       <dees-tile>
         <div slot="header" class="header">
@@ -460,98 +593,25 @@ export class DeesTable<T> extends DeesElement {
                 <thead>
                   ${this.renderHeaderRows(effectiveColumns)}
                 </thead>
-                <tbody>
+                <tbody
-                  ${viewData.map((itemArg, rowIndex) => {
+                  @click=${this.__onTbodyClick}
-                    const getTr = (elementArg: HTMLElement): HTMLElement => {
+                  @dblclick=${this.__onTbodyDblclick}
-                      if (elementArg.tagName === 'TR') {
+                  @mousedown=${this.__onTbodyMousedown}
-                        return elementArg;
+                  @contextmenu=${this.__onTbodyContextmenu}
-                      } else {
+                  @dragenter=${this.__onTbodyDragenter}
-                        return getTr(elementArg.parentElement!);
+                  @dragleave=${this.__onTbodyDragleave}
-                      }
+                  @dragover=${this.__onTbodyDragover}
-                    };
+                  @drop=${this.__onTbodyDrop}
+                >
+                  ${useVirtual && topSpacerHeight > 0
+                    ? html`<tr aria-hidden="true" style="height:${topSpacerHeight}px"><td></td></tr>`
+                    : html``}
+                  ${renderRows.map((itemArg, sliceIdx) => {
+                    const rowIndex = renderStart + sliceIdx;
+                    const rowId = this.getRowId(itemArg);
                     return html`
                       <tr
-                        @click=${(e: MouseEvent) => this.handleRowClick(e, itemArg, rowIndex, viewData)}
+                        data-row-idx=${rowIndex}
-                        @mousedown=${(e: MouseEvent) => {
-                          // Prevent the browser's native shift-click text
-                          // selection so range-select doesn't highlight text.
-                          if (e.shiftKey && this.selectionMode !== 'single') e.preventDefault();
-                        }}
-                        @dragenter=${async (eventArg: DragEvent) => {
-                          eventArg.preventDefault();
-                          eventArg.stopPropagation();
-                          const realTarget = getTr(eventArg.target as HTMLElement);
-                          setTimeout(() => {
-                            realTarget.classList.add('hasAttachment');
-                          }, 0);
-                        }}
-                        @dragleave=${async (eventArg: DragEvent) => {
-                          eventArg.preventDefault();
-                          eventArg.stopPropagation();
-                          const realTarget = getTr(eventArg.target as HTMLElement);
-                          realTarget.classList.remove('hasAttachment');
-                        }}
-                        @dragover=${async (eventArg: DragEvent) => {
-                          eventArg.preventDefault();
-                        }}
-                        @drop=${async (eventArg: DragEvent) => {
-                          eventArg.preventDefault();
-                          const newFiles: File[] = [];
-                          for (const file of Array.from(eventArg.dataTransfer!.files)) {
-                            this.files.push(file);
-                            newFiles.push(file);
-                            this.requestUpdate();
-                          }
-                          const result: File[] = this.fileWeakMap.get(itemArg as object);
-                          if (!result) {
-                            this.fileWeakMap.set(itemArg as object, newFiles);
-                          } else {
-                            result.push(...newFiles);
-                          }
-                        }}
-                        @contextmenu=${async (eventArg: MouseEvent) => {
-                          // If the right-clicked row isn't part of the
-                          // current selection, treat it like a plain click
-                          // first so the context menu acts on a sensible
-                          // selection (matches file-manager behavior).
-                          if (!this.isRowSelected(itemArg)) {
-                            this.selectedDataRow = itemArg;
-                            this.selectedIds.clear();
-                            this.selectedIds.add(this.getRowId(itemArg));
-                            this.__selectionAnchorId = this.getRowId(itemArg);
-                            this.emitSelectionChange();
-                            this.requestUpdate();
-                          }
-                          const userItems: plugins.tsclass.website.IMenuItem[] =
-                            this.getActionsForType('contextmenu').map((action) => ({
-                              name: action.name,
-                              iconName: action.iconName as any,
-                              action: async () => {
-                                await action.actionFunc({
-                                  item: itemArg,
-                                  table: this,
-                                });
-                                return null;
-                              },
-                            }));
-                          const defaultItems: plugins.tsclass.website.IMenuItem[] = [
-                            {
-                              name:
-                                this.selectedIds.size > 1
-                                  ? `Copy ${this.selectedIds.size} rows as JSON`
-                                  : 'Copy row as JSON',
-                              iconName: 'lucide:Copy' as any,
-                              action: async () => {
-                                this.copySelectionAsJson(itemArg);
-                                return null;
-                              },
-                            },
-                          ];
-                          DeesContextmenu.openContextMenuWithOptions(eventArg, [
-                            ...userItems,
-                            ...defaultItems,
-                          ]);
-                        }}
                         class="${itemArg === this.selectedDataRow || this.isRowSelected(itemArg) ? 'selected' : ''}"
                       >
                         ${this.showSelectionCheckbox
@@ -574,7 +634,6 @@ export class DeesTable<T> extends DeesElement {
                               : value;
                             const editKey = String(col.key);
                             const isEditable = !!(col.editable || col.editor);
-                            const rowId = this.getRowId(itemArg);
                             const isFocused =
                               this.__focusedCell?.rowId === rowId &&
                               this.__focusedCell?.colKey === editKey;
@@ -591,26 +650,7 @@ export class DeesTable<T> extends DeesElement {
                             return html`
                               <td
                                 class=${cellClasses}
-                                @click=${(e: MouseEvent) => {
+                                data-col-key=${editKey}
-                                  if (isEditing) {
-                                    e.stopPropagation();
-                                    return;
-                                  }
-                                  if (isEditable) {
-                                    this.__focusedCell = { rowId, colKey: editKey };
-                                  }
-                                }}
-                                @dblclick=${(e: Event) => {
-                                  const dblAction = this.dataActions.find((actionArg) =>
-                                    actionArg.type?.includes('doubleClick')
-                                  );
-                                  if (isEditable) {
-                                    e.stopPropagation();
-                                    this.startEditing(itemArg, col);
-                                  } else if (dblAction) {
-                                    dblAction.actionFunc({ item: itemArg, table: this });
-                                  }
-                                }}
                               >
                                 <div class="innerCellContainer">
                                   ${isEditing ? this.renderCellEditor(itemArg, col) : content}
@@ -646,15 +686,20 @@ export class DeesTable<T> extends DeesElement {
                         })()}
                       </tr>`;
                   })}
+                  ${useVirtual && bottomSpacerHeight > 0
+                    ? html`<tr aria-hidden="true" style="height:${bottomSpacerHeight}px"><td></td></tr>`
+                    : html``}
                 </tbody>
               </table>
               </div>
               <div class="floatingHeader" aria-hidden="true">
-                <table>
+                ${this.__floatingActive
-                  <thead>
+                  ? html`<table>
-                    ${this.renderHeaderRows(effectiveColumns)}
+                      <thead>
-                  </thead>
+                        ${this.renderHeaderRows(effectiveColumns)}
-                </table>
+                      </thead>
+                    </table>`
+                  : html``}
               </div>
             `
           : html` <div class="noDataSet">No data set!</div> `}
@@ -771,7 +816,8 @@ export class DeesTable<T> extends DeesElement {
   // ─── Floating header (page-sticky) lifecycle ─────────────────────────
   private __floatingResizeObserver?: ResizeObserver;
   private __floatingScrollHandler?: () => void;
-  private __floatingActive = false;
+  // __floatingActive is declared as a @state field above so its toggle
+  // triggers re-rendering of the floating-header clone subtree.
   private __scrollAncestors: Array<{ target: Element | Window; scrollsY: boolean; scrollsX: boolean }> = [];
 
   private get __floatingHeaderEl(): HTMLDivElement | null {
@@ -854,32 +900,45 @@ export class DeesTable<T> extends DeesElement {
 
   private setupFloatingHeader() {
     this.teardownFloatingHeader();
-    if (this.fixedHeight) return;
+    // Skip entirely only when neither feature needs scroll watchers.
+    if (this.fixedHeight && !this.virtualized) return;
     const realTable = this.__realTableEl;
     if (!realTable) return;
 
     this.__scrollAncestors = this.__collectScrollAncestors();
     // .tableScroll is a descendant (inside our shadow root), not an ancestor,
-    // so the upward walk above misses it. Add it explicitly so horizontal
+    // so the upward walk above misses it. Add it explicitly. In Mode A
-    // scrolling inside the table re-syncs the floating header.
+    // (`fixedHeight`) it is the only vertical scroll source — mark it as
+    // scrollsY in that case so virtualization picks it up.
     const tableScrollEl = this.shadowRoot?.querySelector('.tableScroll') as HTMLElement | null;
     if (tableScrollEl) {
-      this.__scrollAncestors.unshift({ target: tableScrollEl, scrollsY: false, scrollsX: true });
+      this.__scrollAncestors.unshift({
+        target: tableScrollEl,
+        scrollsY: this.fixedHeight,
+        scrollsX: true,
+      });
     }
 
     // Track resize of the real table so we can mirror its width and column widths.
     this.__floatingResizeObserver = new ResizeObserver(() => {
-      this.__syncFloatingHeader();
+      if (!this.fixedHeight) this.__syncFloatingHeader();
+      if (this.virtualized) this.__computeVirtualRange();
     });
     this.__floatingResizeObserver.observe(realTable);
 
-    this.__floatingScrollHandler = () => this.__syncFloatingHeader();
+    this.__floatingScrollHandler = () => {
+      if (!this.fixedHeight) this.__syncFloatingHeader();
+      // Recompute virtual range on every scroll — cheap (one rect read +
+      // some math) and necessary so rows materialize before they're seen.
+      if (this.virtualized) this.__computeVirtualRange();
+    };
     for (const a of this.__scrollAncestors) {
       a.target.addEventListener('scroll', this.__floatingScrollHandler, { passive: true });
     }
     window.addEventListener('resize', this.__floatingScrollHandler, { passive: true });
 
-    this.__syncFloatingHeader();
+    if (!this.fixedHeight) this.__syncFloatingHeader();
+    if (this.virtualized) this.__computeVirtualRange();
   }
 
   private teardownFloatingHeader() {
@@ -898,35 +957,99 @@ export class DeesTable<T> extends DeesElement {
     if (fh) fh.classList.remove('active');
   }
 
+  // ─── Virtualization ─────────────────────────────────────────────────
+
+  /**
+   * Computes the visible row range based on the table's position in its
+   * nearest vertical scroll ancestor (or the viewport). Updates
+   * `__virtualRange` if it changed; that triggers a Lit re-render.
+   */
+  private __computeVirtualRange() {
+    if (!this.virtualized) return;
+    const view: T[] = (this as any)._lastViewData ?? [];
+    const total = view.length;
+    if (total === 0) {
+      if (this.__virtualRange.start !== 0 || this.__virtualRange.end !== 0) {
+        this.__virtualRange = { start: 0, end: 0 };
+      }
+      return;
+    }
+    const realTable = this.__realTableEl;
+    if (!realTable) return;
+    const tableRect = realTable.getBoundingClientRect();
+
+    // Find the innermost vertical scroll ancestor (rect + content height).
+    let viewportTop = 0;
+    let viewportBottom = window.innerHeight;
+    for (const a of this.__scrollAncestors) {
+      if (a.target === window || !a.scrollsY) continue;
+      const r = (a.target as Element).getBoundingClientRect();
+      const cs = getComputedStyle(a.target as Element);
+      const bt = parseFloat(cs.borderTopWidth) || 0;
+      const bb = parseFloat(cs.borderBottomWidth) || 0;
+      viewportTop = Math.max(viewportTop, r.top + bt);
+      viewportBottom = Math.min(viewportBottom, r.bottom - bb);
+    }
+
+    const rowH = Math.max(1, this.__rowHeight);
+    // Distance from the table top to the visible window top, in px of body
+    // content (so any header offset above the rows is excluded).
+    const headerHeight = realTable.tHead?.getBoundingClientRect().height ?? 0;
+    const bodyTop = tableRect.top + headerHeight;
+    const offsetIntoBody = Math.max(0, viewportTop - bodyTop);
+    const visiblePx = Math.max(0, viewportBottom - Math.max(viewportTop, bodyTop));
+
+    const startRaw = Math.floor(offsetIntoBody / rowH);
+    const visibleCount = Math.ceil(visiblePx / rowH) + 1;
+    const start = Math.max(0, startRaw - this.virtualOverscan);
+    const end = Math.min(total, startRaw + visibleCount + this.virtualOverscan);
+
+    if (start !== this.__virtualRange.start || end !== this.__virtualRange.end) {
+      this.__virtualRange = { start, end };
+    }
+  }
+
+  /**
+   * Measures the height of the first rendered body row and stores it for
+   * subsequent virtualization math. Idempotent — only measures once per
+   * `data`/`columns` pair (cleared in `updated()` when those change).
+   */
+  private __measureRowHeight() {
+    if (!this.virtualized || this.__rowHeightMeasured) return;
+    const tbody = this.shadowRoot?.querySelector('tbody') as HTMLTableSectionElement | null;
+    if (!tbody) return;
+    const firstRow = Array.from(tbody.rows).find((r) => r.hasAttribute('data-row-idx'));
+    if (!firstRow) return;
+    const h = firstRow.getBoundingClientRect().height;
+    if (h > 0) {
+      this.__rowHeight = h;
+      this.__rowHeightMeasured = true;
+    }
+  }
+
   /**
    * Single function that drives both activation and geometry of the floating
-   * header. Called on scroll, resize, table-resize, and after each render.
+   * header. Called on scroll, resize, table-resize, and after relevant
+   * renders.
+   *
+   * Activation is decided from the *real* header geometry, so this function
+   * works even when the clone subtree hasn't been rendered yet (it's only
+   * rendered when `__floatingActive` is true). The first activation flips
+   * `__floatingActive`; the next render materializes the clone; the next
+   * call here mirrors widths and positions.
    */
   private __syncFloatingHeader() {
     const fh = this.__floatingHeaderEl;
     const realTable = this.__realTableEl;
-    const floatTable = this.__floatingTableEl;
+    if (!fh || !realTable) return;
-    if (!fh || !realTable || !floatTable) return;
 
     const tableRect = realTable.getBoundingClientRect();
     const stick = this.__getStickContext();
-
-    // Mirror table layout + per-cell widths so columns line up.
-    floatTable.style.tableLayout = realTable.style.tableLayout || 'auto';
     const realHeadRows = realTable.tHead?.rows;
-    const floatHeadRows = floatTable.tHead?.rows;
     let headerHeight = 0;
-    if (realHeadRows && floatHeadRows) {
+    if (realHeadRows) {
-      for (let r = 0; r < realHeadRows.length && r < floatHeadRows.length; r++) {
+      for (let r = 0; r < realHeadRows.length; r++) {
         headerHeight += realHeadRows[r].getBoundingClientRect().height;
-        const realCells = realHeadRows[r].cells;
-        const floatCells = floatHeadRows[r].cells;
-        for (let c = 0; c < realCells.length && c < floatCells.length; c++) {
-          const w = realCells[c].getBoundingClientRect().width;
-          (floatCells[c] as HTMLElement).style.width = `${w}px`;
-          (floatCells[c] as HTMLElement).style.minWidth = `${w}px`;
-          (floatCells[c] as HTMLElement).style.maxWidth = `${w}px`;
-        }
       }
     }
 
@@ -938,9 +1061,34 @@ export class DeesTable<T> extends DeesElement {
     if (shouldBeActive !== this.__floatingActive) {
       this.__floatingActive = shouldBeActive;
       fh.classList.toggle('active', shouldBeActive);
+      if (shouldBeActive) {
+        // Clone subtree doesn't exist yet — wait for the next render to
+        // materialize it, then complete geometry sync.
+        this.updateComplete.then(() => this.__syncFloatingHeader());
+        return;
+      }
     }
     if (!shouldBeActive) return;
 
+    // Mirror table layout + per-cell widths so columns line up. The clone
+    // exists at this point because __floatingActive === true.
+    const floatTable = this.__floatingTableEl;
+    if (!floatTable) return;
+    floatTable.style.tableLayout = realTable.style.tableLayout || 'auto';
+    const floatHeadRows = floatTable.tHead?.rows;
+    if (realHeadRows && floatHeadRows) {
+      for (let r = 0; r < realHeadRows.length && r < floatHeadRows.length; r++) {
+        const realCells = realHeadRows[r].cells;
+        const floatCells = floatHeadRows[r].cells;
+        for (let c = 0; c < realCells.length && c < floatCells.length; c++) {
+          const w = realCells[c].getBoundingClientRect().width;
+          (floatCells[c] as HTMLElement).style.width = `${w}px`;
+          (floatCells[c] as HTMLElement).style.minWidth = `${w}px`;
+          (floatCells[c] as HTMLElement).style.maxWidth = `${w}px`;
+        }
+      }
+    }
+
     // Position the floating header. Clip horizontally to the scroll context
     // so a horizontally-scrolled inner container's header doesn't bleed
     // outside the container's border.
@@ -970,24 +1118,55 @@ export class DeesTable<T> extends DeesElement {
 
   public async updated(changedProperties: Map<string | number | symbol, unknown>): Promise<void> {
     super.updated(changedProperties);
-    this.determineColumnWidths();
+
-    // (Re)wire the floating header whenever the relevant props change or
+    // Only re-measure column widths when the data or schema actually changed
-    // the table markup may have appeared/disappeared.
+    // (or on first paint). `determineColumnWidths` is the single biggest
+    // first-paint cost — it forces multiple layout flushes per row.
+    const dataOrColsChanged =
+      !this.__columnsSizedFor ||
+      this.__columnsSizedFor.data !== this.data ||
+      this.__columnsSizedFor.columns !== this.columns;
+    if (dataOrColsChanged) {
+      this.__columnsSizedFor = { data: this.data, columns: this.columns };
+      this.determineColumnWidths();
+      // Force re-measure of row height; structure may have changed.
+      this.__rowHeightMeasured = false;
+    }
+
+    // Virtualization: measure row height after the first paint with rows,
+    // then compute the visible range. Both ops only run when `virtualized`
+    // is true, so the cost is zero for normal tables.
+    if (this.virtualized) {
+      this.__measureRowHeight();
+      this.__computeVirtualRange();
+    }
+
+    // (Re)wire the scroll watchers (used by both the floating header in
+    // Mode B and by virtualization). Skip entirely only when neither
+    // feature needs them.
     if (
       changedProperties.has('fixedHeight') ||
+      changedProperties.has('virtualized') ||
       changedProperties.has('data') ||
       changedProperties.has('columns') ||
       !this.__floatingScrollHandler
     ) {
-      if (!this.fixedHeight && this.data.length > 0) {
+      const needsScrollWatchers = (!this.fixedHeight || this.virtualized) && this.data.length > 0;
+      if (needsScrollWatchers) {
         this.setupFloatingHeader();
       } else {
         this.teardownFloatingHeader();
       }
     }
-    // Keep the floating header in sync after any re-render
+    // Only sync the floating header geometry when it's actually showing or
-    // (column widths may have changed).
+    // the table layout-affecting state changed. Avoids per-render layout
-    if (!this.fixedHeight && this.data.length > 0) {
+    // reads (getBoundingClientRect on every header cell) for typical updates
+    // like sort changes or selection toggles.
+    if (
+      !this.fixedHeight &&
+      this.data.length > 0 &&
+      (this.__floatingActive || dataOrColsChanged)
+    ) {
       this.__syncFloatingHeader();
     }
     if (this.searchable) {
@@ -1502,6 +1681,187 @@ export class DeesTable<T> extends DeesElement {
     this.requestUpdate();
   }
 
+  // ─── Delegated tbody event handlers ─────────────────────────────────
+  // Hoisted from per-<tr> closures to a single set of handlers on <tbody>.
+  // Cuts ~7 closure allocations per row per render. Each handler resolves
+  // the source row via `data-row-idx` (and `data-col-key` for cell-level
+  // events) using the latest `_lastViewData`.
+
+  private __resolveRow(eventArg: Event): { item: T; rowIdx: number } | null {
+    const path = (eventArg.composedPath?.() || []) as EventTarget[];
+    let tr: HTMLTableRowElement | null = null;
+    for (const t of path) {
+      const el = t as HTMLElement;
+      if (el?.tagName === 'TR' && el.hasAttribute('data-row-idx')) {
+        tr = el as HTMLTableRowElement;
+        break;
+      }
+    }
+    if (!tr) return null;
+    const rowIdx = Number(tr.getAttribute('data-row-idx'));
+    const view: T[] = (this as any)._lastViewData ?? [];
+    const item = view[rowIdx];
+    if (!item) return null;
+    return { item, rowIdx };
+  }
+
+  private __resolveCell(eventArg: Event): { item: T; rowIdx: number; col: Column<T> } | null {
+    const row = this.__resolveRow(eventArg);
+    if (!row) return null;
+    const path = (eventArg.composedPath?.() || []) as EventTarget[];
+    let td: HTMLTableCellElement | null = null;
+    for (const t of path) {
+      const el = t as HTMLElement;
+      if (el?.tagName === 'TD' && el.hasAttribute('data-col-key')) {
+        td = el as HTMLTableCellElement;
+        break;
+      }
+    }
+    if (!td) return null;
+    const colKey = td.getAttribute('data-col-key')!;
+    const cols = this.__getEffectiveColumns();
+    const col = cols.find((c) => String(c.key) === colKey);
+    if (!col) return null;
+    return { item: row.item, rowIdx: row.rowIdx, col };
+  }
+
+  private __isInActionsCol(eventArg: Event): boolean {
+    const path = (eventArg.composedPath?.() || []) as EventTarget[];
+    for (const t of path) {
+      const el = t as HTMLElement;
+      if (el?.classList?.contains('actionsCol')) return true;
+    }
+    return false;
+  }
+
+  private __isInEditor(eventArg: Event): boolean {
+    const path = (eventArg.composedPath?.() || []) as EventTarget[];
+    for (const t of path) {
+      const el = t as HTMLElement;
+      const tag = el?.tagName;
+      if (tag === 'INPUT' || tag === 'TEXTAREA' || el?.isContentEditable) return true;
+      if (tag && tag.startsWith('DEES-INPUT-')) return true;
+    }
+    return false;
+  }
+
+  private __onTbodyClick = (eventArg: MouseEvent) => {
+    if (this.__isInEditor(eventArg) || this.__isInActionsCol(eventArg)) return;
+    const cell = this.__resolveCell(eventArg);
+    if (!cell) return;
+    const view: T[] = (this as any)._lastViewData ?? [];
+    // Cell focus (when editable)
+    if (cell.col.editable || cell.col.editor) {
+      this.__focusedCell = {
+        rowId: this.getRowId(cell.item),
+        colKey: String(cell.col.key),
+      };
+    }
+    // Row selection (file-manager style)
+    this.handleRowClick(eventArg, cell.item, cell.rowIdx, view);
+  };
+
+  private __onTbodyDblclick = (eventArg: MouseEvent) => {
+    if (this.__isInEditor(eventArg) || this.__isInActionsCol(eventArg)) return;
+    const cell = this.__resolveCell(eventArg);
+    if (!cell) return;
+    const isEditable = !!(cell.col.editable || cell.col.editor);
+    if (isEditable) {
+      eventArg.stopPropagation();
+      this.startEditing(cell.item, cell.col);
+      return;
+    }
+    const dblAction = this.dataActions.find((a) => a.type?.includes('doubleClick'));
+    if (dblAction) dblAction.actionFunc({ item: cell.item, table: this });
+  };
+
+  private __onTbodyMousedown = (eventArg: MouseEvent) => {
+    // Suppress browser's native shift-click text selection so range-select
+    // doesn't highlight text mid-table.
+    if (eventArg.shiftKey && this.selectionMode !== 'single') eventArg.preventDefault();
+  };
+
+  private __onTbodyContextmenu = (eventArg: MouseEvent) => {
+    if (this.__isInActionsCol(eventArg)) return;
+    const row = this.__resolveRow(eventArg);
+    if (!row) return;
+    const item = row.item;
+    // Match file-manager behavior: right-clicking a non-selected row makes
+    // it the selection first.
+    if (!this.isRowSelected(item)) {
+      this.selectedDataRow = item;
+      this.selectedIds.clear();
+      this.selectedIds.add(this.getRowId(item));
+      this.__selectionAnchorId = this.getRowId(item);
+      this.emitSelectionChange();
+      this.requestUpdate();
+    }
+    const userItems: plugins.tsclass.website.IMenuItem[] = this.getActionsForType('contextmenu').map(
+      (action) => ({
+        name: action.name,
+        iconName: action.iconName as any,
+        action: async () => {
+          await action.actionFunc({ item, table: this });
+          return null;
+        },
+      })
+    );
+    const defaultItems: plugins.tsclass.website.IMenuItem[] = [
+      {
+        name:
+          this.selectedIds.size > 1
+            ? `Copy ${this.selectedIds.size} rows as JSON`
+            : 'Copy row as JSON',
+        iconName: 'lucide:Copy' as any,
+        action: async () => {
+          this.copySelectionAsJson(item);
+          return null;
+        },
+      },
+    ];
+    DeesContextmenu.openContextMenuWithOptions(eventArg, [...userItems, ...defaultItems]);
+  };
+
+  private __onTbodyDragenter = (eventArg: DragEvent) => {
+    eventArg.preventDefault();
+    eventArg.stopPropagation();
+    const row = this.__resolveRow(eventArg);
+    if (!row) return;
+    const tr = (eventArg.composedPath?.() || []).find(
+      (t) => (t as HTMLElement)?.tagName === 'TR'
+    ) as HTMLElement | undefined;
+    if (tr) setTimeout(() => tr.classList.add('hasAttachment'), 0);
+  };
+
+  private __onTbodyDragleave = (eventArg: DragEvent) => {
+    eventArg.preventDefault();
+    eventArg.stopPropagation();
+    const tr = (eventArg.composedPath?.() || []).find(
+      (t) => (t as HTMLElement)?.tagName === 'TR'
+    ) as HTMLElement | undefined;
+    if (tr) tr.classList.remove('hasAttachment');
+  };
+
+  private __onTbodyDragover = (eventArg: DragEvent) => {
+    eventArg.preventDefault();
+  };
+
+  private __onTbodyDrop = async (eventArg: DragEvent) => {
+    eventArg.preventDefault();
+    const row = this.__resolveRow(eventArg);
+    if (!row) return;
+    const item = row.item;
+    const newFiles: File[] = [];
+    for (const file of Array.from(eventArg.dataTransfer!.files)) {
+      this.files.push(file);
+      newFiles.push(file);
+      this.requestUpdate();
+    }
+    const existing: File[] | undefined = this.fileWeakMap.get(item as object);
+    if (!existing) this.fileWeakMap.set(item as object, newFiles);
+    else existing.push(...newFiles);
+  };
+
   /**
    * Handles row clicks with file-manager style selection semantics:
    *  - plain click: select only this row, set anchor